My 2 cents:
First, normally when tires go onto a Hunter GSP9700, the operator first checks to see if the road force value is excessive.
What's excessive? My experience says that varies a lot with the locale and the operator. With sophisticated operators, it will also vary according to the type of vehicle (which is another way of saying with the type of tire). However, there are built in tolerances to the machine, which are frequently used by less sophisticated operators.
When an excessive value is encountered, there is a procedure to check the wheel. Unless the bare wheel is measured (rarely!), the runout of the wheel is measured using the wheel flanges. The value obtained this way is somewhat suspect, but because it is fairly easy to do and generally produces reasonable results, most folks rely on it.
Further it indicates a low point of the wheel which can be used to line up with the high point of the tire to obtain a "more round" assembly. The machine will tell the operator where these points are and predicts a value if done. This helps the operator decide if it is worth the trouble.
Note, that there is a procedure to measure a bare wheel and that is a whole lot more accurate, but it is time consuming!
Originally Posted By: Traction
I've always wondered about another potential problem, that no wheel balancer can check under load, at 80+ MPH. If you had a perfectly round, balanced wheel, and had a round tire, but it takes an excessive amount weight to balance out a heavy spot in the tread of the tire. I would think the centrifugal force of many pounds from the surface of the tire, would cause that section to stretch outwards, thumping the road, and eventually wear it out round, and then be out for balance again?
Traction,
Road Force has nothing whatsoever to do with balance. It has to do with the combination of stiffness and runout - commonly called *Uniformity*.
But once a tire is balanced, it is balanced for 2 mph and 200 mph. The only difference would be the weight increments needed to balance with a tolerance necessary for the speed. My experience says that the 1/4 ounce (5 grams) is more than adequate for up to 80 mph - and maybe more.
Further, balance is not really dependent on the load on the tire.
HOWEVER, Road Force (Uniformity) is not only speed dependent it is also load dependent. The problem is that tires not only change amount at high speed, but the high point also changes location at high speeds. The one thing that can be said is that tires with low, low speed values yield low, high speed values, and tires with his high, low speed values are unpredictable.
Further, since the diameter of the wheel on the machine is fairly small, it tends to emphasize small duration events, while de-emphasizing long duration events. That is, the machine can give both high values for a tire assembly that is really a low value assembly, and vice versa.
With all of that said, that is why I say the Hunter GSP9700 is a great diagnostic tool, but not necessarily a good screening tool. Not only can the machine cause a good assembly to be rejected, but it can accept a bad assembly.
My experience also says that balance and uniformity aren't big contributors to irregular wear - but alignment is. There have been a number of studies where perfectly balanced assemblies with low uniformity values will turn into high uniformity tires based on the amount of toe.
First, normally when tires go onto a Hunter GSP9700, the operator first checks to see if the road force value is excessive.
What's excessive? My experience says that varies a lot with the locale and the operator. With sophisticated operators, it will also vary according to the type of vehicle (which is another way of saying with the type of tire). However, there are built in tolerances to the machine, which are frequently used by less sophisticated operators.
When an excessive value is encountered, there is a procedure to check the wheel. Unless the bare wheel is measured (rarely!), the runout of the wheel is measured using the wheel flanges. The value obtained this way is somewhat suspect, but because it is fairly easy to do and generally produces reasonable results, most folks rely on it.
Further it indicates a low point of the wheel which can be used to line up with the high point of the tire to obtain a "more round" assembly. The machine will tell the operator where these points are and predicts a value if done. This helps the operator decide if it is worth the trouble.
Note, that there is a procedure to measure a bare wheel and that is a whole lot more accurate, but it is time consuming!
Originally Posted By: Traction
I've always wondered about another potential problem, that no wheel balancer can check under load, at 80+ MPH. If you had a perfectly round, balanced wheel, and had a round tire, but it takes an excessive amount weight to balance out a heavy spot in the tread of the tire. I would think the centrifugal force of many pounds from the surface of the tire, would cause that section to stretch outwards, thumping the road, and eventually wear it out round, and then be out for balance again?
Traction,
Road Force has nothing whatsoever to do with balance. It has to do with the combination of stiffness and runout - commonly called *Uniformity*.
But once a tire is balanced, it is balanced for 2 mph and 200 mph. The only difference would be the weight increments needed to balance with a tolerance necessary for the speed. My experience says that the 1/4 ounce (5 grams) is more than adequate for up to 80 mph - and maybe more.
Further, balance is not really dependent on the load on the tire.
HOWEVER, Road Force (Uniformity) is not only speed dependent it is also load dependent. The problem is that tires not only change amount at high speed, but the high point also changes location at high speeds. The one thing that can be said is that tires with low, low speed values yield low, high speed values, and tires with his high, low speed values are unpredictable.
Further, since the diameter of the wheel on the machine is fairly small, it tends to emphasize small duration events, while de-emphasizing long duration events. That is, the machine can give both high values for a tire assembly that is really a low value assembly, and vice versa.
With all of that said, that is why I say the Hunter GSP9700 is a great diagnostic tool, but not necessarily a good screening tool. Not only can the machine cause a good assembly to be rejected, but it can accept a bad assembly.
My experience also says that balance and uniformity aren't big contributors to irregular wear - but alignment is. There have been a number of studies where perfectly balanced assemblies with low uniformity values will turn into high uniformity tires based on the amount of toe.
